14 DAY TRIAL // Did our species still evolve in the last 10 000 years? Scientists now have a clear proof that the answer is yes. We haven't just developed culturally and technologically, but also biologically. While the cultural and technological development took the form of actively changing the environment to fit our desires, the biological evolution consisted in the organism's adaptation to the changing external environment.
The mechanism of biological evolution consists on one hand in random genetic mutations and on the other hand in the environment favoring some genes over the others. In other words, in the context of a certain external environment, people having some genes are more probable to have children and to perpetuate their genes.
Researchers from the University of Chicago analyzed the genomes of 209 unrelated individuals from three distinct human populations: East Asians, Europeans and Yorubans from Nigeria. They have found that evolution in the last 10 millennia favored certain genes over the others, but that most of the affected genes differed depending on the group.
"There have been a lot of recent changes - the advent of agriculture, shifts in diet, new habitats, climatic changes - over the past 10,000 years," said Jonathan Pritchard, the human geneticist at the University of Chicago who led this study. These major events have influenced the human biology. "It's reasonable to suspect that a lot of these [genetic changes] are adaptations in response to new diets and agriculture," said Pritchard.
Scientists found certain changes that affected all the studied human populations and some which were group specific. For example, the study showed that four previously unknown pigment genes causing European lighter skin have changed. The change was an adaptation to the lack of sunlight. Interestingly, the study found that a certain mutation many East Asians have, a mutation in the genes involved in the production of alcohol dehydrogenase (ADH), a protein necessary for breaking down of alcohol, was in fact positively reinforced by natural selection. This signifies that this mutation, besides preventing these people to metabolize alcohol, probably has some yet unknown benefit.
What about the genes that evolved in all groups? Researchers have identified 700 positively genes evolving under the positive selection of the environment and many of them are among the ones that undergone natural selection during the divergence of humans and chimpanzees millions of years ago.
The authors write: "Our analysis of the types of genes involved in recent selection provides a first insight into the type of biological processes that have been targets of selection in the latest stages of our evolution. Some of these functions (especially olfaction and fertilization-related genes) have also been found to show signals of sustained selection over much longer evolutionary timescales. However, other classes of selected genes (for example the skin pigmentation genes and metabolic genes) likely reflect the process of adaptation to modern conditions and new environments. Nonetheless, gaining a full view of the kinds of selective pressures that have faced modern humans, and our biological adaptations to those pressures, remains a challenging problem. For many selective signals there is uncertainty about the actual genetic target. Even when the target is clear, the nature of the adaptation is often not. Hence, interpreting the story of human adaptation promises to be an interesting research area for years to come."
Although the specific functions of many genes are not known, the genes which have been positively selected can nevertheless be grouped into several categories. LiveScience described the following:
￭ Olfaction: the researchers found many genes important for taste and smell ￭ Reproduction: involved in things like sperm mobility and egg fertilization ￭ Increasing brain size ￭ Bone development and skeletal changes ￭ Carbohydrate metabolism: positive selection was observed for genes involved in breaking down mannose in Yorubans, sucrose in East Asians, and lactose for Europeans. (Mannose is a sweet secretion found in some trees and shrubs, sucrose is common table sugar, and lactose is a sugar found in milk.) ￭ Disease resistance and pathogen protection ￭ Metabolism of foreign compounds, such as exotic plant proteins or animal toxins
"There is ample evidence that selection has been a major driving point in our evolution during the last 10,000 years, and there is no reason to suppose that it has stopped," said Pritchard.